Bob up Definition 1 of 2Pro Tip 1/3Unexpected Situations Use 'bob up' to express that something happened without warning or foresight. I had everything planned, but then a new problem bobbed up. Pro Tip 2/3Sudden Visibility 'Bob up' illustrates someone or something suddenly coming into view or attention. In the middle of the discussion, an old memory bobbed up. Pro Tip 3/3Impromptu Opportunities Use 'bob up' when speaking about unexpected chances cropping up. Keep your eyes open; a great opportunity might just bob up.